Oreo is a brand of sandwich cookie consisting of two cocoa biscuits or cookie pieces with a sweet fondant filling. It was introduced by Nabisco on March 6, 1912, and through a series of corporate acquisitions, mergers, and splits, both Nabisco and the Oreo brand have been owned by Mondelez since 2012. Oreo cookies are available in over one hundred countries. Many varieties of Oreo cookies have been produced, and limited-edition runs have become popular in the 21st century.

Oreos are an imitation of the Hydrox chocolate cream-centered cookie introduced in 1908, but it outstripped Hydrox in popularity so largely that many believe Hydrox is an imitation of Oreo. Oreo has been the highest-selling cookie brand in the world since 2014